LOS ANGELES, May 13 (Xinhua) -- Combining observations from NASA's Hubble and Spitzer space telescopes, astronomers have spotted a distant "warm Neptune" has an atmosphere rich with hydrogen, helium and water vapor and evidence of exotic clouds.

About 437 light-years away from Earth, the Neptune-sized exoplanet, dubbed HAT-P-26b, circles a star roughly twice as old as the sun, reveals a study published in the May 12, 2017 issue of Science.

HAT-P-26b's atmosphere is relatively clear of clouds and has a strong water signature, although the planet is not a water world. This is the best measurement of water to date on an exoplanet of this size, according to NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California.

And the analysis is also one of the most detailed studies to date of a "warm Neptune," or a alien planet that is Neptune-sized and close to its star.

The study "shows that there is a lot more diversity in the atmospheres of these exoplanets than we were expecting, which is providing insight into how planets can form and evolve differently than in our solar system," David K. Sing, an astrophysics professor at the University of Exeter in England and the co-leader of the new study, said in a statement.

Compared to Neptune and Uranus, the alien world's closest counterparts in our own solar system in terms of mass, HAT-P-26b likely formed either closer to its host star or later in the development of its planetary system, or both.

The discovery of an atmosphere with this composition on this exoplanet has implications for how scientists think about the birth and development of planetary systems, researchers say.

"Astronomers have just begun to investigate the atmospheres of these distant Neptune-mass planets, and almost right away, we found an example that goes against the trend in our solar system," said Hannah Wakeford, lead author of the study, said.

"This kind of unexpected result is why I really love exploring the atmospheres of alien planets."